1. Field of the Invention
The present invention relates to a belt tension adjusting device, and more particularly to a device for adjusting the tension state of a transmission belt of an optical scanning apparatus.
2. Description of the Prior Art
Please refer to FIG. 1. FIG. 1 illustrates a prior art drive system 10 taught in U.S. Pat. No. 5,106,345 by Moore et al, which is herein incorporated by reference. The drive system 10 includes a belt 26 having teeth 28 adapted to engage gears 36 and 38 in a device such as a printer or a scanner. The system also includes a tensioner 32 which applies tension to the belt 26.
Please refer to FIG. 2 and FIG. 3. FIG. 2 and FIG. 3 are schematic diagrams of a resilient means 148 for maintaining proper tension in a drive belt 136. The resilient means 148 is taught in U.S. Pat. No. 5,323,407 by Wolf et al, which is herein incorporated by reference. The resilient means 148 may comprise a coiled spring 150 having a first hook portion 152 extending from one end of the coiled spring 150 and a second hook portion 154 extending from the other end of the coiled spring 150. The first hook portion 152 has a first linear portion 156 integral with the coiled spring 150, a second linear portion 158 integral with and extending in a direction substantially perpendicular to the first linear portion 156 and a hook extension 160 integral with and extending in a direction substantially perpendicular to the second linear portion 158. The second hook portion 154 has a first linear portion 162 integral with the coiled spring 150, a second linear portion 164 integral with and extending in a direction substantially perpendicular to the first linear portion 162 and a hook extension 166 integral with and extending in a direction substantially perpendicular to the second linear portion 164.
The operational relationship between a portion 168 of the drive belt 136 and the resilient means 148 is illustrated in FIG. 3. The portion 168 passes under the second linear portion 158, over the coiled spring 150 and under the second linear portion 164. As it passes under the second linear portions 158 and 164, the portion 168 is located between a portion of the first linear portions 156 and 162 and a portion of the hook extensions 160 and 166.
The frictional forces generated by the force of the coiled spring 150 urging the second linear portions 158 and 164 against the surface of the portion 168 of the drive belt 136 will be enough to prevent any substantial relative movement between the portion 168 and the second linear portions 158 and 164. However, to ensure against any substantial relative movement, the surface of the second linear portions 158 and 164 contacting the portion 168 could be provided with a friction generating rib or roughened surface. Similarly, the belt portion 168 could be provided with a ribbed or other friction increasing surface. In operation, any slackness occurring in the other portions of the drive belt 136 would permit the second linear portions 158 and 164 to move toward each other while still maintaining a substantially constant tension on the drive belt 136. Also, any shortening in other portions of the drive belt 136, such as caused by a change in temperature, would cause the second linear portions 158 and 164 to move away from each other while still maintaining a substantially constant tension on the belt.
Please refer to FIG. 4 and FIG. 5. FIG. 4 and FIG. 5 show two common ways of adjusting the tension of transmission belts of scanners. In FIG. 4, a slide block pulley type is shown. It comprises a slide block 52, a spring 51, a belt 53, a carrier 54, and pulleys 55. FIG. 5 shows a rocker arm adjusting type, which includes an adjusting wheel 63, a spring 51, a belt 53, pulleys 55, a rocker arm 62, a carrier 54, a scanner frame 71, a glass surface 72, and a document 73. In both types as shown in FIG. 4 and FIG. 5, either slide blocks or rocker arms are required. This may cause damage to the belt, and the belt may become loosened, causing the transmission state of the transmission belt to slide during adjustment. Besides, the moving parts may wear, resulting in deflection of the tension of the transmission belt and defective transmission. In addition, there are numerous parts and components, which means increase in costs and reduction in competitiveness. All of these are problems that need to be solved.